1. Field of the Invention
The present invention relates to semiconductor fabrication and, more particularly, to a photosensitive polymer and a chemically amplified resist composition.
2. Description of the Related Art
As the manufacture of semiconductor devices becomes complicated and the integration density of semiconductor devices highly increases, there is a need to form a fine pattern. Furthermore, with regard to semiconductor devices having a memory capacity of 1-Gigabit or more, a pattern size having a design rule of 0.1 μm or less is needed.
When a conventional photoresist material is exposed with KrF excimer laser (248 nm), however, it is difficult to form such fine patterns. For this reason, a lithography technique using a new exposure light source, ArF excimer laser (193 nm) or F2 (157 nm) excimer laser, has been actively researched. Specifically, for the lithography using a short-wavelength generating F2 (157 nm) excimer laser, a resist material with a novel structure is required.
Polymer materials used in the lithography using F2 (157 nm) excimer laser are required to meet the following requirements: (1) high transparency for 157 nm light source; (2) high resistance against a plasma used during a dry etching process; (3) good adhesion to the underlying layers to avoid pattern collapse; and (4) capability of being developed using a conventional developer.
There are several limitations in satisfying the above requirements. Particularly, polymer materials may have very low transparency and a very weak resistance against a dry etching process.
To date, several resist materials for next-generation F2 excimer laser have been found and various researches into fluorinated polymers and siloxane polymers have been made. In particular, because fluorinated polymers have excellent transmittance at 157 nm, they are vigorously being studied as next-generation resist materials. These materials are, however, difficult to synthesize monomers. And polymers synthesized therefrom have too strong hydrophobicity. Thus, it is difficult to find suitable structures as resist materials.
As one of resist materials for 157 nm laser, a polynorbornene copolymer having the following formula was proposed as follows. 
The copolymer having the above structural formula has good adhesion and dry etching resistance characteristics. The copolymer, however, also potentially suffers from drawbacks. Specifically, it is difficult to adjust the molecular weight in synthesizing polymers, and it is also difficult to remove impurities produced due to use of metallic catalyst.
Another conventional resist material is a copolymer of α-trifluoromethylacrylic monomer and a styrene derivative, as disclosed in Proc. SPIE, Vol. 4345, 273-284 (2001), the copolymer having a structural formula as follows. 
The above-referenced report suggested that a fluorinated aromatic compound having the above structure could be suitably as a thin-film resist material at 157 nm. However, this compound has still several drawbacks. In particular, there is a need for polymers having a high transmittance and improved dry etching resistance.